1. Field of the Invention
The present invention relates to an ink jet printer head having a plurality of pressure chambers arranged in a plurality of arrays, and to a method of inspecting the ink jet printer head about whether the arrays of pressure chambers are fluid-tightly isolated from each other.
2. Discussion of Related Art
For example, Japanese Patent Application Publication No. 2001-260349 or its corresponding U.S. Pat. No. 6,604,817 discloses a conventional piezoelectric ink jet printer head including a channel unit constituted by a plurality of sheet members which are stacked on each other via adhesive; a piezoelectric actuator which is bonded to a back surface of the channel unit; and a flexible flat cable which is stacked on, and bonded to, a back surface of the piezoelectric actuator, for electrically connecting the actuator to an external device.
The above-indicated channel unit includes a nozzle sheet having a plurality of ink ejection nozzles opening in a front surface of the printer head; a base sheet having a plurality of pressure chambers communicating with the ink ejection nozzles, respectively; and a manifold sheet and another or other sheet members having a common ink chamber (i.e., a manifold chamber) connected to an ink supply source, and a plurality of ink channels connected to the pressure chambers, respectively. The nozzle sheet, the base sheet, the manifold sheet and the other sheet members are stacked on, and adhered to, each other. In this printer head, when an active portion of the piezoelectric actuator that corresponds to an arbitrary one of the pressure chambers of the channel unit is deformed in a direction parallel to the direction of stacking of the sheet members, a droplet of ink is ejected from the arbitrary pressure chamber via the corresponding ink ejection nozzle, so that a desired image is printed or recorded on a recording medium such as a sheet of paper.
Meanwhile, there has been proposed an ink jet printer head whose channel unit has an increased number of ink ejection nozzles arranged in a plurality of arrays, for the purpose of increasing the speed and/or density of printing (i.e., recording) of the printer head, and/or for the purpose of printing a full-color image. FIG. 6 shows an upper surface of a base sheet 117 of a channel unit of the conventional ink jet printer head. The base sheet 117 has a plurality of pressure chambers 136 which are formed through a thickness of the sheet 117 such that the pressure chambers 136 are arranged in a plurality of arrays (only three arrays are shown) corresponding to a plurality of arrays in which a plurality of ink ejection nozzles 104 are arranged. The base sheet 117 additionally has a plurality of ink supply holes 160 (160a, 160b, 160c, . . . ) formed through the thickness thereof. The channel unit has a plurality of common ink chambers (i.e., manifold chambers) 107 which are elongate in a lengthwise direction of the channel unit and are connected to the ink supply holes 160, respectively; a plurality of communication holes 138 arranged in a plurality of arrays; and a plurality of through-holes 137 arranged in a plurality of arrays. The arrays of pressure chambers 136 extend along the common ink chambers 107, respectively, in the lengthwise direction of the channel unit. A plurality of kinds of color inks are supplied to the common ink chambers 107, respectively, via the respective ink supply holes 160, and then each of the color inks is delivered from a corresponding one of the common ink chambers 107 to respective one end portions of the pressure chambers 136 if a corresponding one of the arrays via the respective communication holes 138. When the ink accommodated by an arbitrary one of the pressure chambers 136 is pressurized by a corresponding active portion of a piezoelectric actuator, not shown, a droplet of the ink is ejected from a corresponding one of the ink ejection nozzles 104 via the other end portion of the arbitrary pressure chamber 136 and a corresponding one of the through-holes 137.
In the above-described ink jet printer head, two closure sheet members are respectively adhered to two opposite planar surfaces of the base sheet 117 having the pressure chambers 136, so that the pressure chambers 136 are fluid-tightly closed by those closure sheet members and are thereby isolated from each other. Those two closure sheet members are a sheet member of the channel unit that is adhered to a lower planar surface of the base sheet 117, and a lowermost sheet member of the piezoelectric actuator that is adhered to an upper planar surface of the base sheet 117. However, if the adhesion of each one of the two closure sheet members to the base sheet 117 is defective, two or more pressure chambers 136 may communicate with each other. In this case, when one of those pressure chambers 136 is pressurized, ink may leak from the one pressure chamber 136 to a location outside the printer head, or to one or two adjacent pressure chambers 136 located adjacent the one pressure chamber 136. This leads to decreasing or lowering an amount and/or a pressure of the ink ejected from the desired ink ejection nozzle 104, and thereby lowering a quality of printing of the printer head. To solve this problem, a process of producing the ink jet printer head employs a step of inspecting whether the sheet members of the channel unit and/or the piezoelectric actuator have been appropriately stacked on, and adhered to, each other such that the pressure chambers 136 are fluid-tightly isolated from each other.
Next, there will be explained various routs in which ink leaks because of the defective adhesion of one or both of the two closure sheet members to the base sheet 117, by reference to the pressure chamber 136c, shown in FIG. 6, as a representative of all the pressure chambers 136. The ink may leak in a first route, indicated by “A”, from the pressure chamber 136c to an outer peripheral edge of the base sheet 117 (i.e., a location outside the printer head); in a second route, indicated by “B”, from the pressure chamber 136c to an adjacent pressure chamber 136d located adjacent the pressure chamber 136c in a same array; or in a third route, indicated by “C”, from the pressure chamber 136c to an adjacent pressure chamber 136e located adjacent the pressure chamber 136c, in an array located adjacent the array in which the pressure chamber 136c is arranged. However, generally, the leakage of ink via the route “A” can be effectively prevented because a considerably large adhesion area can be provided between each pressure chamber 136 and the outer peripheral edge of the base sheet 117 and additionally one or more adhesive pouring grooves and/or one or more adhesive relieving grooves can be formed in the adhesion area. The leakage of ink via the route “B” does not adversely influence the quality of printing so much, because a pitch of arrangement of the pressure chambers 136 in a same array is very small and additionally a same kind of ink is accommodated by those pressure chambers 136. On the other hand, the leakage of ink via the route “C” may cause a problem of mixture of different kinds of color inks, because a distance between two adjacent arrays of pressure chambers 136 is considerably large and the different kinds of color inks are accommodated by the different arrays of pressure chambers 136, respectively.
Thus, the above-indicated step of inspecting the fluid-tight isolation of the pressure chambers 136 is arranged such that after the piezoelectric actuator is bonded to the upper surface of the channel unit (hereinafter, this will be referred to as the bonded body), all the ink ejection nozzles 104 are temporarily fluid-tightly closed, and a pressurized air is supplied to each one of the ink supply holes 160. If air leaks from any of the pressure chambers 136 of, e.g., the first array 161a that communicate with the first ink supply hole 160a via the corresponding common ink chamber 107, then the pressure of the pressurized air will lower. Thus, the fluid-tight isolation of the pressure chambers 136 can be inspected by measuring the pressure of the pressurized air after a prescribed time period has elapsed. If the leakage of the pressurized air is detected, i.e., the isolation of the pressure chambers 136 is found defective, then the bonded body is discarded and is not conveyed to any subsequent steps.